Method of making glass from reacted and shaped batch materials

ABSTRACT

THIS SPECIFICATION DISCLOSES A CONTINUOUS, BATCH OR SEMIBATCH PROCESS FOR MAKING GLASS AND PARTICULARLY BUT NOT LIMITED TO SO-CALLED SODA-LIME GLASS COMPRISING IN A CONTINUOUS MANNER PREPARING A SUBSTANTIALLY REACTED GLASS MAKING BATCH WHEREIN AN ALKALI METAL HYDROXIDE IS EMPLOYED AS A CONSTITUENT THEREOF TO PROVIDE A SOURCE OF AT LEAST 50 PERCENT OF THE ALKALI METAL FLUX VALUES IN THE FINAL GLASS, FORMING SAID BATCH INTO A CONTINUOUS OR DISCONTINUOUS ELONGATED SHAPE, DRYING SAID BATCH SO-ELONGATED, AND THEREAFTER PASSING THE DRIED RIGID SHAPED BATCH INTO A HIGH TEMPERATURE ZONE TO RAPIDLY AND CONTINUOUSLY MELT THE ELONGATED BATCH AND FINE IT. THE MOLTEN GLASS SO MADE CAN BE SOLIDFIED OR WORKED INTO A USEFUL CONFIGURATION.   D R A W I N G

April 6, 1971 w. A. MOD ETAL 3,573,887

METHOD OF MAKING GLASS FROM REACTED AND SHAPED BATCH MATERIALS FiledFeb. 27, 1968 fi/ka/ine ear/h me/o/ 0 x l'de sou/c 6 Minor if)?! 8076!)6 2 Sheets-Sheet 2 Glass form er O//7er a/ka/l' mefa/ ox/ae source (/2any) H/ka/imefa/ hydroxide so/u/fon Mixer re0cfar- /1 INVENTORS.Dona/0Q. C0/0we// BY W/Y/lam 6. M00

HTTORNEYS United States Patent O 3,573,887 METHOD OF MAKING GLASS FROMREACTED AND SHAPED BATCH MATERIALS William A. Mod and Donald L.Caldwell, Lake Jackson,

Tex., assignors to The Dow Chemical Company, Midland, Mich.

Filed Feb. 27, 1968, Ser. No. 708,673 Int. 1. C031) 1/00 US. CI. 65-1811 Claims ABSTRACT OF THE DISCLOS This specification discloses acontinuous, batch or semibatch process for making glass and particularlybut not limited to so-called soda-lime glass comprising in a continuousmanner preparing a substantially reacted glass making batch wherein analkali metal hydroxide is employed as a constituent thereof to provide asource of at least 50 percent of the alkali metal flux values in thefinal glass, forming said batch into a continuous or discontinuouselongated shape, drying said batch so-elongated, and thereafter passingthe dried rigid shaped batch into a high temperature zone to rapidly andcontinuously melt the elongated batch and fine it. The molten glass somade can be solidified or worked into a useful configuration.

BACKGROUND OF THE INVENTION This invention relates to making glass andmore particularly relates to preparing essentially seed-free glass in anear-instantaneous manner.

Current glass-making practice utilizes a large glass melting tank(furnace) in which a glass making batch is melted and fined for up to 48hours to allow gases to escape and the melt to become homogeneous. Themelting tank generally comprises a two-compartment refractory bricklined vessel separated by a bafiie which is attached to a ceiling orcrown and dips into the pool of molten glass. In one chamber the batchis introduced and heated by various means including jets of ignitedglass to melt it, whereupon, the melted material passes the bafile intoa second chamber where it is fined to permit release of gas bubbles,etc. Molten fined glass is then withdrawn from the discharge end of thefurnace as gobs which are then cast or blown or manipulated into auseful shape such as bottles and solidified, or wherein the glass may bedrawn from the furnace and formed into sheets. Such a melting tankrepresents a very large capital expense and a large maintenance problem.Usually, after being in operation for about 2 to 5 years, the facilitymust be shut down to repair or rebuild it.

A particular maintenance problem encountered in such a furnace resultsfrom decrepitation of the calcium carbonate component of the glass batchupon being exposed to the elevated temperatures in the glass makingprocess. Decrepitation is the bursting or popping of the carbonateparticle into finer particles due to the extremely rapid calcination orevolution of gasses therefrom. These fine particles are carried by gasstreams and flames playing about the furnace into the regenerativecheckers where they deposit to plug the checkers. This pluggingnecessitates at least partial shutdowns so that the checkers may becleaned, which is a disruptive and time consuming operation. Increasedfurnace temperatures of course increases the output of glass, however,the furnace life is markedly decreased.

A further problem with respect to gases in the melting furnace is thepresence of seeeds or voids in the final glass product which may hinderthe usefulness of such product.

The terms final glass or final glass product as used 3,573,887 PatentedApr. 6, 1971 herein refers to a final glass composition ordinarily used,for example, for windows and bottles having a silica content generallybetween about 60 and 85 percent by weight, preferably from 68 topercent, and alkali flux values (Na O and K 0 primarily) between about 4and 20 percent, including the so-called soda lime glasses having between10 and 20 percent alkali flux as well as the chemical and heat resistantborosilicate glasses ranging in silica and boric oxide from about to 93percent and in alkali fiuxes from about 4 to about 10 percent, thecommon stabilizing and modifying oxides, e.g., alumina, calcia,magnesia, and lead oxide essentially making up the remainingconstituents.

The term alkaline earth metal oxide source as used herein refers toalkaline earth metal compounds which will furnish alkaline earth metaloxide values in the final glass product and includes sources such aslimestone, dolomite, calcined limestone, calcined dolomite, CaCO andCa(OH) The term alkali metal oxide source as used herein refers toalkali metal compounds which will furnish alkali metal oxide values inthe final glass product and includes sources such as sodium hydroxide,potassium hydroxide, sodium carbonate, and potassium carbonate.

In conventional soda-lime glass making practice, a number of finelysized raw materials which make up the glass making batch are weighed,mixed, and transported to the glass melting furnace. The composition ofa batch in addition to the glass-forming materials, typically containsby weight from about 15 to about 35 percent of an alkali metalcarbonate, such as sodium carbonate (soda ash), as a primary source ofalkali metal flux oxides in the resulting glass product and sometimes aslow as 10 and as high as about 40 percent alkali metal carbonate. Thebatch also contains alkaline earth metal carbonates typically, calciumcarbonate, as CaO-source materials and other stabilizers, in an amountto provide from about 8 to about 14 percent of C in the final glassproduct and preferably 9.5 to 11.5 percent CaO in said product. Thebalance of the batch is a glass forming material such as silica, andsmall amounts of other agents designed to impart a particular effect.

A primary object of the present invention is to provide a novel methodof making glass wherein the conventional glass melting tank with all itsattendant maintenance and operational disadvantages may be eliminated.

Another primary object of the present invention is to provide a noveland unique method of making glass wherein the melting and fining of aglass batch may be accomplished in a matter of minutes as opposed tohours in the conventional method.

A further object of the invention is to provide an extremely rapidmethod for the melting and fining of sodalime and borosilicate glassbatches to produce a final glass composition substantially free ofseeds.

Another object of the invention is to provide a novel method of makingglass which can be completely shut down in a matter of a few minuteswithout a large residual invenory of melted and/or partially meltedglass in a furnace.

SUMMARY OF THE INVENTION In accordance with the present invention theabove and other objects and advantages are found in a unique and novelmethod for making in a rapid manner a final glass product without theneed of employing the conventional glass melting furnaces consisting ofthe following combination of process steps, conditions and limitations.First, a homogeneous glass making raw material batch is preparedcontaining (a) one or more glass formers such as, e.g., silica sand, (b)a stabilizing, alkaline earth metal oxide source material such as, e.g.,a calcium oxide-containing substance such as calcium carbonate, (c)various modifying oxides, and (d) as a source of at least 50 percent ofthe alkali metal flux values in a final glass product, preferably 100percent, an alkali metal hydroxide such as, e.g., sodium hydroxide as a45 to 80 percent aqueous solution thereof. The batch preferably containsan alkaline earth metal source material present in an amount from about10 to about 40 weight percent, an alkali metal oxide source material inan amount from about 15 to about 35 percent, the balance being at leastone glass former. The homogeneous batch is then subjected to atemperature in the range of, e.g., of from about 60 to about 215 C.while concurrently, or subsequently, formed preferably into an elongatedshape such as by extrusion or casting into a bar, to cause substantialreaction between the sta bilizing oxide source material and the alkalimetal hydroxide. In a dried substantially rigid shape, the reacted batchis exposed in a continuous manner to an elevated temperature zone, e.g.,greater than 1400 C., where the glass batch is rapidly melted and fined.The molten fined glass may either be worked in the hot condition asreceived from the high temperature zone into a useful configuration, orsolidified and stored for future use. The proccess may be carried out ina batch, semibatch, or con tinuous manner to prepare in a matter ofminutes from a raw composition a final fined glass product, having avery low seed count without the use of a conventional large inventoryglass melting tank typically requiring several hours to produce a finalglass product from a glass batch.

The present invention will be further understood and illustrated fromthe accompanying drawings.

FIG. 1 is a schematic drawing of one embodiment of the presentinvention.

FIG. 2 is a schematic drawing of another embodiment of the presentinvented method.

In carrying out the present invention, there are various embodimentsthereof which may be employed wherein particular changes andmodifications may be employed regarding the sequence, consolidation, andaddition or deletion of certain process steps.

PREFERRED EMBODIMENTS One particular embodiment of the inventive processconsists essentially of the sequence as schematically depicted in FIG. 1of the drawings. In this embodiment, a glass former, e.g., SiO astabilizing, alkaline earth metal oxide source, e.g., CaCO in an amountsuificient to pro vide from about 8 to 13 percent stabilizing oxide inthe final glass product; an aqueous solution of an alkali metalhydroxide, e.g., 45 to 80 percent aqueous solution of NaOH, in an amountsufiicient to provide at least 50 percent of the alkali metal oxide inthe final glass product; other alkali metal oxide source materials,e.g., Na CO if necessary, and other conventional minor glass batchconstituents are admixed and reacted in a mixer-reactor 1 at about 60 to215 C. for about to 60 minutes. The reacted mixture is discharged into afeed hopper 2 from which it is fed into a glass extruder 3 where themixture is extruded into continuous or discontinuous elongated shaped,e.g., bars or rods 4. These solidified shapes or pieces 4 are fed into ahot zone 5 maintained at a temperature within the range of 1600 to 1700C. by induction coils 6 and susceptor 7, i.e., conductor, or similarheating means, e.g., an oxygen-methane burner. Optionally, thesolidified pieces may be dried by a conventional dryer 20 and storedprior to further processing. Since the upper end of the hot zone acts asa dryer, a separate dryer is unnecessary where a continuous process isemployed. The elongated pieces 4 melt and fine in the hot zone 5 in amatter of seconds producing a homogeneous glass melt. Optionally, themelt may be cooled, e.g., about 1200 C. in a cooling zone 8 usingcooling coils 9 or other conventional cooling means. The molten glass iscut into modules of gobs 11 by shears or other cutting means and fed toa utilization device 12, e.g., bottle or other containermakingapparatus. Alternatively, the molten glass can be fed, e.g., into asingle or multiple opening orifice to produce glass fibers or strands.Optionally, the molten glass can be collected in a reservoir 25 prior touse.

Another embodiment of the method of the present invention is depicted inFIG. 2. The reacted mixture as ,heretofore defined in connection withFIG. 1 is fed into a manifold 30 which feeds the mixture to one or morefeed hoppers 2, depending on production requirements. The glass mixtureis then processed as previously explained with respect to FIG. 1 and theaccompanying discussion.

As can be readily seen from the drawings and the above description theprocess of the present invention permits rapid glass manufacture withoutlarge residual melted glass and without the need for the conventionalmelting tank, thereby avoiding such problems as periodic shutdowns forcleaning necessitated by decrepitation as heretofore explained.

The following example is representative of the method of the presentinvention but is not intended to be limited thereto.

EXAMPLE Dry ingredients of a commercial-type soda-lime glass Theingredients were thoroughly mixed and brought to a temperature of 60 C.and 156.5 grams of commercial grade 50% NaOH aqueous solution was added.The mixing was continued for about 25' minutes and brought to atemperature of 70 C. The moist batch was cast into diameter rods bypacking into small metal tubes about 6" long. The so-cast rods werefurther reacted and dried by heating at C. The rods were removed fromthe molds and were suspended so the lower end of the rods (one at atime) could be lowered through the center of a one inch ring of anoxygen-natural gas burner, providing a temperature in excess of 1400 C.As each rod was fed into the hot zone, the batch melted within secondsand beads of glass were formed which could be drawn off as strands, cutoff as small lumps, or allowed to fall as beads.

In like manner any conventional soda-lime or borosilicate glass batchhaving as at least a 50 percent alkali metal oxide source an alkalimetal hydroxide, e.g., NaOH or KOH, may be processed according to themethod of the present invention to produce an essentially seed-freefinal glass product.

As heretofore described, the method of the present invention permitscontinuous, near-instantaneous glass manufacture without the use ofconventional glass tank equipment thereby eliminating conventionalmaintenance and operational disadvantages.

Various modifications can be made in the present invention withoutdeparting from the scope or spirit thereof, for it is to be understoodthat the invention is limited only as defined in the appended claims.

What is claimed is:

1. A method of making glass which comprises:

(a) reacting a homogeneous raw materials glass batch containing at leastone glass former selected from the group consisting of silica and boricoxide sources, an alkaline earth metal oxide source material, and analkali metal oxide source material, said alkali metal oxide sourcematerial containing an alkali metal hydroxide selected from the groupconsisting of sodium hydroxide and potassium hydroxide in an amountsufficient to provide at least 50% of the alkali metal oxide value inthe glass; said reaction carried out at a temperature of from about 60C. to about 215 C. for a time suflicient to substantially react thealkaline earth metal oxide source with the alkali metal hydroxide;

(b) forming an elongated shape of said reacted glass batch; suspendingsaid elongated shape in a vertical orientation, and

(c) continuously passing a lower end of said suspended elongated glassbatch shape downwardly through a hot zone having a temperature of atleast 1400 0., thereby producing a molten, fined glass from said lowerend of said suspended glass batch.

2. The method of claim 1 wherein the alkali metal hydroxide is presentas about a 45 to 80 percent aqueous solution.

3. The method of claim 1 wherein the alkaline earth metal sourcematerial is present in an amount of from about to about 40 weightpercent, the alkali metal oxide source material being from about toabout weight percent, the balance being at least one glass former.

4. The method of claim 1 wherein in step (c) the temperature in the hotzone is within the range of from about 1600 C. to 1700 C.

5. The method of claim 1 wherein the alkali metal hydroxide is a 100percent source of the alkali metal oxide value on the final glassproduct.

6. The method of claim 1 wherein the alkali metal hydroxide is sodiumhydroxide.

6 7. The method of claim 1 wherein in step (a) the batch is reacted forfrom about 5 to about minutes.

8 The method of claim 1 wherein in step (b) the reacted glass batch isformed into an elongated shape References Cited UNITED STATES PATENTS2,838,882 6/1958 Silverman 18X 3,234,034 2/1966 Jasinski et al 10652X3,451,831 6/1969 Miche 10652 FOREIGN PATENTS 670,974 9/1963 Canada 65-18S. LEON BASHORE, Primary Examiner J. B. HARDAWAY, Assistant Examiner US.Cl. X.R.

